Concentricity Gauges and Neck Turning?

engineer40

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While doing some research I came across some ideas that are new to me in regards to reloading for accuracy.

This guy used a concentricity gauge to measure a few things. The most important being once the bullet has been seated to make sure it is completely even all around. The other a little less important he said he measures the wall thickness of his brass and he will put a small mark on the thinnest side of his brass. When shooting, he then lines that mark up with a lug on his bolt. (This is obviously not possibly if hunting and ammo is in the magazine).

Another thing he was very adamant about was neck turning. It provides an even neck thickness all the way around. It also helps to distort the case neck less when reloading/resizing.

Are both of these worth of the effort and will they actually produce better results? I'm not opposed to purchasing the tools and putting in the time if these are known proven accuracy tactics.

Thank you!
 

Mikecr

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For every notion in reloading there are qualifiers associated.
With straight ammo & neck turning, the qualifier is chamber clearances.

Where you have sloppy fitting of heavily FL sized ammo, runout contributes nothing to results. So it could be suggested that loose chambers are a workaround for runout, and I believe this is a reason many seem happier with results from loose chamber fit.

Those with tighter clearances could find that runout matters.
The reason runout can be detrimental for tighter chambers is chambered tensions created by crooked ammo. It doesn't matter so much where bullets are pointed initially(we'll never know that), but where bullets end up pointed as the banana straightens under early pressure. Chambered tension points are also analogous to other tension points(w/resp to barrel vibrations). Rest a thumb on an action tang mid-string to see what this can do.
 

Mikecr

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Making straight ammo involves more than necks.
Because of the way brass cases are made, thickness variance as seen at a neck runs full length of the case. Thickness variance = spring back variance. We add energy to brass when we size, and this is where spring back variance bows cases like a banana. So the only way to stop growing runout with each FL sizing, is to first cull out cases with any thickness variance at all.

With less & less sizing, runout grows at a slower rate. Those with fitted cases, that don't size them at all, will never see any runout -except that caused at necks and by bullet seating.
Neck turning removes thickness variance (in necks), and with this they'll spring back away from chamber neck evenly, to leave a nice round hole for straight bullet seating.
There are ways people screw up straight necks with their sizing. Dies and bushings and presses aren't perfect. Many have issues with their expander system. Mandrels are often better where there is excess sizing going on.
Wilson type inline dies remove the press from addition.

Of course there are other reasons for/against each attribute of neck turning & sizing in general.
 

engineer40

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Rockford, MI
Thanks Mikecr! I appreciate the explanation.

I did notice that the expander plug in my full length resize die seems to really "catch" the brass on the upswing. I'll need to look into that. Because now I'm definitely thinking that is distorting the case neck more than it needs to be.

My collet neck resizer feels a lot better. But I'm curious if because I FL resize new brass if it throws the case neck out of alignment right away...
 
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